1. Field of the Invention
The present invention relates to an ink, and an ink-jet recording method and instruments making use of the ink. In particular, the present invention relates to an ink which can achieve high-speed, highly fine and high-image quality, full-color recording on non-coated paper such as paper for electrophotography, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, to say nothing of coated paper specially prepared for ink-jet recording, and an ink-jet recording method and instruments making use of such an ink.
2. Related Background Art
In an image-forming process by an ink-jet recording system, there has been a demand, as one of techniques which have increasingly acquired an importance in recent years, for development of an ink for image recording and an image-forming process which permit highly fine, full-color recording, which is good in color development and free from any feathering or bleeding, even on non-coated paper such as paper for electrophotography, paper for reporting, notepaper, letter paper, bond paper and continuous business forms (these will hereinafter be called "plain paper" collectively), which are commonly used in offices and homes. Many proposals have been made with a view toward achieving such an demand.
For example, Japanese Patent Application Laid-Open No. 55-29546 discloses a process for enhancing the penetrability of an ink into a paper sheet, in which a specific surfactant is added to the ink to lower the surface tension of the ink. It is also disclosed in Japanese Patent Application Laid-Open No. 55-57862 to add a strongly basic substance to an ink so as to chemically dissolve a sizing agent and pulp contained in a paper sheet, thereby controlling the areas of dots and the easiness of absorption.
Further, Japanese Patent Application Laid-Open No. 58-13675 discloses the addition of polyvinylpyrrolidone having a molecular weight of not less than 40,000 to an ink, or Japanese Patent Application Laid-Open No. 3-172362 discloses a method of controlling the areas of dots and the easiness of absorption by adding a specific microemulsion to an ink.
Furthermore, U.S. Pat. Nos. 3,653,932, 3,715,219, 4,390,369 and 4,490,731 separately disclose a solid-liquid phase-change ink, i.e., an ink which is solid at room temperature, but turns liquid at a specified temperature or higher. The phase-change ink of this type is ejected as a liquid and then struck against a recording material to immediately solidify on the surface of the recording material.
As examples of the use of a gel-sol transition ink, inks that are in a gel state at room temperature, but change into a sol state under heat are disclosed in Japanese Patent Application Laid-Open Nos. 62-181372 and 1-272623, etc. As with the solid-liquid phase-change ink, these inks are all intended to change again into the gel state after their impact against recording materials to suppress the running of the inks.
However, the above-mentioned techniques involve such problems as described below.
The method of enhancing the penetrability of an ink by the addition of a surfactant can improve the fixability of the ink, but involves a problem that since a recording agent also penetrates deeply, the color-producing property of the ink is lowered.
The method in which a strongly basic substance is added to an ink is insufficient to solve problems of both running and fixability against paper making use of a certain size, for example, medium-quality paper, and also has a problem of safety for human body.
Further, the mere addition of a polymer or a certain emulsion to an ink fails to exhibit sufficient effects in such a range that recording density of the ink becomes greater upon full-color recording or the like.
Furthermore, the solid-liquid phase-change type ink requires to liquefy the ink upon operation, and hence involves such problems that the ink makes the burden to apparatus such as the temperature control of an ink feed system heavier, and moreover, when the print is exposed to, for example, an extremely high temperature during its storage, the ink remelts, resulting in deformation of printed areas.
As with the solid-liquid phase-change ink, the sol-gel transition ink is also difficult to handle and has a problem of shelf stability in prints.
As described above, various proposals have been made with a view toward improving ink-jet recording properties to plain paper. However, there has not yet been known an ink which has good color-producing property to plain paper, does not cause problems of bleeding and feathering even when impacting at least two inks on the same area, is excellent in fixability, and makes the burden to apparatus light.